Introduce a basic Blink Scheduler

Source/platform/ThreadTimers.cpp

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 #include "config.h"
 #include "platform/ThreadTimers.h"
 
+#include "platform/PlatformThreadData.h"
 #include "platform/SharedTimer.h"
-#include "platform/PlatformThreadData.h"
 #include "platform/Timer.h"
 #include "platform/TraceEvent.h"
+#include "platform/scheduler/Scheduler.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/MainThread.h"
 
 using namespace std;
 
 namespace WebCore {
 
 // Fire timers for this length of time, and then quit to let the run loop process user input events.
 // 100ms is about a perceptable delay in UI, so use a half of that as a threshold.
 // This is to prevent UI freeze when there are too many timers or machine performance is low.
@@ skipping 87 matching lines @@
         timer.setNextFireTime(interval ? fireTime + interval : 0);
 
         TRACE_EVENT2("blink", "ThreadTimers::sharedTimerFiredInternal",
             "src_file", timer.location().fileName(),
             "src_func", timer.location().functionName());
 
         // Once the timer has been fired, it may be deleted, so do nothing else with it after this point.
         timer.fired();
 
         // Catch the case where the timer asked timers to fire in a nested event loop, or we are over time limit.
-        if (!m_firingTimers || timeToQuit < monotonicallyIncreasingTime())
+        if (!m_firingTimers || timeToQuit < monotonicallyIncreasingTime() || (isMainThread() && Scheduler::current()->shouldYieldForHighPriorityWork()))

[eseidel, 2014/07/15 15:59:11]

Do we ever have a sharedTimer not on the main thread?  I'm surprised
isMainThread() is necessary here.

[Sami, 2014/07/15 19:20:05]

We don't have a shared timer there, but can have a ThreadTimers instance on a
non-main thread. See the initialization in ThreadTimers::ThreadTimers().

             break;
     }
 
     m_firingTimers = false;
 
     updateSharedTimer();
 }
 
 void ThreadTimers::fireTimersInNestedEventLoop()
 {
     // Reset the reentrancy guard so the timers can fire again.
     m_firingTimers = false;
     updateSharedTimer();
 }
 
 } // namespace WebCore